Scientific Report 2005

Immunology

The Consequences of T-Cell Recognition of Self-Antigens and Tumor Antigens

L.A. Sherman, H.T.C. Kreuwel, W.L. Redmond, M.A. Lyman, C.H. Wei, J.A. Biggs, K.L. Marquardt, R.L. Trenney, J. Martinez, B. Marincek

The consequence of antigen recognition by naive CD8⁺ T cells can be either tolerance or immunity, depending on the activation status of the antigen-presenting dendritic cells. If a CD8⁺ cell recognizes antigen on a quiescent dendritic cell that expresses relatively low levels of costimulatory molecules, then activation of the T cell results in deletion and tolerance. Inflammatory signals, such as those due to the presence of foreign pathogens and activated lymphocytes, activate dendritic cells to express cell-surface costimulatory molecules and cytokines. If CD8⁺ T cells recognize antigen on activated dendritic cells, the costimulatory molecules and cytokines prevent deletion and promote the clonal expansion of the CD8⁺ cells and the development of effector functions.

Understanding the signals that result in either T-cell deletion or immunity is of importance in preventing autoimmunity, which represents a failure to control self-destructive T lymphocytes. This understanding is also important in promoting tumor immunity, in which the goal is to promote the autoimmune destruction of tumor cells. We are comparing the consequence of the interaction of naive CD8⁺ T lymphocytes with a transgenic self-antigen (the influenza virus hemagglutinin) expressed by the insulin-producing beta cells in the pancreatic islets in 3 different types of mice: normal mice (Ins-HA mice), diabetes-prone nonobese diabetic mice (NOD-InsHA mice) and mice in which the beta cells express an oncogene that promotes spontaneous transformation and production of tumors (RIP-Tag2-InsHA mice).

In all 3 types of mice, the interaction between antigen and naive CD8⁺ T lymphocytes specific for hemagglutinin first occurs in the pancreatic lymph nodes. There, antigen is recognized on dendritic cells that obtain it from beta cells in the islets and cross-present it to naive T cells in the lymph nodes. In normal mice, this interaction results in an abortive activation of the T cells and subsequent deletion of the potentially autoreactive T cells specific for hemagglutinin.

Deletion of Naive CD8⁺ T Cells

Using the transgenic animals that were our source of naive CD8⁺ T cells specific for hemagglutinin, we examined the requirements for peripheral deletion in vivo. We found that independent of the amount of antigen used for stimulation, a single dose of antigen did not result in complete clonal deletion. Instead, further antigenic exposure was required to completely eliminate all of the activated T cells. Consecutive stimulations with low doses of antigen were highly effective in promoting deletion. In contrast, although stimulation with high doses of antigen initially led to the programmed cell death of many of the activated T cells, it induced hyporesponsiveness in part of the responding cells, thereby sparing the cells from further activation and deletion. These data explain why some conditions promote tolerance through clonal deletion whereas others promote anergy. Furthermore, the data provide a framework for devising protocols for effective deletion of potentially autoreactive T cells.

Restoration of CD8⁺ T-Cell Tolerance in NOD Mice

The development of autoimmune diseases such as type 1 diabetes is mediated by multiple genetic and environmental factors. Although genes that may control type 1 diabetes can now be identified, defining the resulting cellular events mediated by each locus is a major challenge. In congenic NOD mice, the genetic regions that control diabetes, designated as insulin-dependent diabetes (Idd) loci, have been replaced by resistant alleles obtained from nondiabetic strains of mice. We hypothesize that critical genetic susceptibility loci regulate the maintenance of self-specific CD8⁺ T cells.

We compared the fate of islet-reactive CD8⁺ and CD4⁺ T cells in diabetes-susceptible NOD mice with the fate of the same kinds of cells in diabetes-resistant NOD congenic mice with protective alleles at Idd3, Idd5.1, and Idd5.2 (Idd3/5 strain) or at Idd9.1, Idd9.2, and Idd9.3 (Idd9 strain). We found that protection from diabetes in each instance is correlated with functional tolerance of islet-specific CD8⁺ T cells; however, this tolerance is achieved in different ways. In Idd3/5 mice, tolerance occurs during the initial activation of islet-specific CD8⁺ and CD4⁺ T cells in the pancreatic lymph nodes, where the presence of CD25⁺ regulatory T cells prevents accumulation of the CD8⁺ and CD4⁺ T cells. In contrast, resistance alleles in Idd9 mice do not prevent the accumulation of islet-specific CD8⁺ and CD4⁺ T cells in the pancreatic lymph nodes, suggesting that tolerance occurs at a later checkpoint. These results underscore the variety of ways that autoimmunity can be prevented and indicate the elimination of islet-specific CD8⁺ T cells as a common indicator of high-level protection.

Fate of Low-Affinity Tumor-Specific CD8⁺ T Cells in Tumor-Bearing Mice

An important issue in tumor immunology is how to best activate and mobilize the low-avidity self-specific and tumor-specific T cells that remain in the T-cell repertoire after the development of central and peripheral tolerance. We generated transgenic mice that express a low-avidity T-cell receptor (clone 1 mice) specific for hemagglutinin, a model self-antigen. When CD8⁺ T cells from clone 1 mice were transferred into InsHA mice, little proliferation occurred in response to low amounts of cross-presented hemagglutinin, indicating that the low-avidity clone 1 CD8⁺ T cells ignore the cross-presented hemagglutinin self-antigen. In contrast, the expression of hemagglutinin as a tumor-associated antigen on spontaneous hemagglutinin-expressing beta cell tumors in RIP-Tag2-InsHA mice led to high levels of cross-presented antigen that could activate the low-affinity clone 1 T cells. However, because of the absence of inflammatory signals, this activation resulted in deletion of the clone 1 cells. This model should be useful in optimizing protocols for immunotherapy of solid tumors with low-affinity tumor-specific T cells.

Publications

Kuball, J., Schmitz, F.W., Voss, R.H., Ferreira, E.A., Engel, R., Guillaume, P., Strand, S., Romero, P., Huber, C., Sherman, L.A., Theobald, M. Cooperation of human tumor-reactive CD4⁺ and CD8⁺ T cells after redirection of their specificity by a high-affinity p53A2.1-specific TCR. Immunity 22:117, 2005.

Lyman, M.A., Nugent, T.C., Marquardt, K.L., Biggs, J.A., Pamer, E.G., Sherman, L.A. The fate of low affinity tumor specific CD8⁺ T cells in tumor-bearing mice. J. Immunol. 174:2563, 2005.

Redmond, W.L., Marincek, B.C., Sherman, L.A. Distinct requirements for deletion versus anergy during CD8 T cell peripheral tolerance in vivo. J. Immunol. 174:2046, 2005.

Redmond, W.L., Sherman, L.A. Peripheral tolerance of CD8 T lymphocytes. Immunity 22:275, 2005.

Yadav, D., Judkowski, V., Flodstrom-Tullberg, M., Sterling, L., Redmond, W.L., Sherman, L., Sarvetnick, N. B7-2 (CD86) controls the priming of autoreactive CD4 T cell response against pancreatic islets. J. Immunol. 173:3631, 2004.